Airplane wing panels, composed of wing skins and generally spanwise extending reinforcing beams or stringers, are constructed on jigs. The stringers are positioned in clamps which, in turn, are attached to jig headers. The surface panels are then fastened to the stringers with conventional fasteners. Because the contour of the wing panels varies in both the spanwise and chordwise directions, the orientation of the stringers relative to the headers will vary slightly but continuously in successive clamping locations in both the spanwise and chordwise directions.
Heretofore, stringer clamps were specially designed and machined for each of the many stringer clamping locations so that the surfaces of an L-shaped portion of the stringers could abut a first clamping surface oriented generally parallel with the wing skin and a second clamping surface oriented generally perpendicular to the chordwise direction relative to the panel. One or both of these clamping surfaces were necessarily machined to a precise angle dictated by the particular clamping position and stringer orientation, so that the stringer surfaces could abut flat clamping surfaces. In an attempt to eliminate some of the machining on one of the surfaces, acruate, plastic inserts have been substituted for the machined surfaces that are parallel to the wing skin. Although satisfactory, the plastic inserts are subject to wear and thus require periodic replacement in order to retain precise alignment of successive sets of stringers relative to the jig.
Intermediate size commercial airplanes have about 250 clamping locations for the upper and lower wing panels for each of the left and right airplane wings, requiring about 500 different clamp configurations in all. The production and marking of that many clamps in accordance with the prior clamping techniques represents a significant investment. It was therefore an overall objective of the present invention to provide a universal stringer clamp that replaces all of the different clamps that would be required if prior clamping techniques were employed. Other objects of the present invention were to eliminate the requisite machining of the clamping surfaces so that they would conform to the precise angles dictated by stringer orientation at each of the clamping locations, to provide a clamp that could alternatively be used at each of the stringer clamping locations and thus eliminate assembly errors that would otherwise result from the use of an incorrect clamp, to provide a clamp that is adjustable and self-aligning, and to provide a clamp that could be locked in its self-aligned position thereafter not requiring realignment when one wing panel was removed from the jig and new stringers positioned on the clamps. And lastly, it was an object of the present invention to achieve the foregoing objectives while producing a more economical and simpler stringer clamp.